Polypropylene has various industrial applications, particularly it is widely applied for materials used in automobiles and electronic products, etc. with various usages. For more expanded applications of polypropylene, an improvement in rigidity which may be led by an increase in the degree of crystallinity is further required.
In order to obtain such properties in polypropylene, it is needed for a solid catalyst for preparing the same to be designed to have high stereoregularity and wide molecular weight distribution.
For polymerization of olefins such as propylene or the like, a solid catalyst comprising magnesium, titanium, an internal electron donor and halogen as essential elements is known in this field of art, and methods for polymerizing or copolymerizing olefins have been proposed many. However, such methods are not satisfying in terms of obtaining polymers having high stereoregularity with a high production yield, and thus needed to be improved in the above aspect.
Silane compounds are usually used as an external electron donor for preventing the stereoregularity from being deteriorated by the release of an internal electron donor from the reaction between a catalyst component and an organoaluminum in propylene polymerization. These may be used for the improvement of bulk density or for inhibiting fine particle generation in catalyst preparation, however the use thereof for the improvement in activity and stereoregularity in catalyst preparation has never known in this field of art.
In the meantime, In order to reduce the production cost by increasing the polymerization activity and improve physical properties of the resulted polymers by improving the catalyst performance such as stereoregularity, it is generally known in this field of art to use diester of aromatic dicarboxylic acid as an internal electron donor and related patent applications have been filed many, for examples, U.S. Pat. Nos. 4,562,173, 4,981,930, Korean Patent No. 0072844 and the like. The above patents describe a method for preparing a catalyst showing high activity and stereoregularity by using aromatic dialkyldiesters or aromatic monoalkylmonoesters.
The methods according to the above-mentioned patents cannot provide satisfying high stereoregular polymers with a high yield and thus further improvements in the methods are required.
Korean Patent No 0491387 discloses a preparation method for a catalyst using a non-aromatic diether as an internal electron donor; Korean Patent No. 0572616 discloses a preparation method for a catalyst using a non-aromatic compound containing both ketone and ether groups as an internal electron donor, however both of said methods are needed to be significantly improved in terms of the activity and stereoregularity.